Virtual video on demand using multiple encrypted video segments

ABSTRACT

A method and apparatus for providing a virtual video on demand services is disclosed. The method and apparatus disclose the storing of a segment of the video program in advance for VOD viewing at a later time. When the subscriber selects VOD service, a pre-stored video segment is retrieved for presentation to the subscriber. Remaining video program segments simultaneously broadcast on a plurality of channels are recorded in parallel while the pre-stored video program segment is retrieved and presented to the user.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/759,679, entitled “VIRTUAL VIDEO ON DEMAND USING MULTIPLE ENCRYPTEDVIDEO SEGMENTS,” by Robert G. Arsenault and Leon J. Stanger, filed Jan.19, 2004, which is a continuation of U.S. patent application Ser. No.09/491,959, entitled “VIRTUAL VIDEO ON DEMAND USING MULTIPLE ENCRYPTEDVIDEO SEGMENTS,” by Robert G. Arsenault and Leon J. Stanger, filed Jan.26, 2000, now issued as U.S. Pat. No. 6,701,528, both of whichapplications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems and methods for providing videoprogram material to subscribers, and in particular to a method andsystem for providing near video on demand services.

2. Description of the Related Art

In recent years, there has been increasing interest in providingvideo-on-demand (VOD) services to cable and satellite televisionsubscribers. With an idealized VOD system, the user simply selects thedesired program material (video or audio), transmits the selection tothe video provider, and the video program is transmitted to the user ina real time data stream. With such idealized systems, the user cancontrol the display of the video program in real time by issuing stop,rewind, fast-forward, or pause commands. These commands are received bythe video server, and the data stream is interrupted or modified asappropriate for the command from the viewer. Essentially, this VODparadigm implements a client-server architecture wherein the user's settop box (or computer) is the client, and the video server is the server.

While the foregoing VOD system would provide the user with beneficialand flexible service, it suffers from several major disadvantages.First, it places tremendous difficulties on the input/output (I/O)multiplexing and bandwidth capabilities of the video server. While thereal-time transmission of a single video program to a single videosubscriber is relatively easy to accomplish, this is not the case when awide variety of different video sources may be requested by a largenumber of video subscribers all at the same time. Essentially, becausesubscriber requests are generally asynchronous, each request for aparticular video program requires a separate transmission, and eachseparate transmission consumes a portion of the available bandwidth.

Second, the foregoing systems are intolerant of communication latenciesbetween the user and the video server. Particularly when fast-forwardingand rewinding through video sequences to look for segments of interest,users may issue a number of commands in rapid succession, expecting nearinstantaneous responses from the video server. Even minor communicationlatencies can become an extreme irritation to the user.

Many different solutions to these problems have been proposed, but forthe most part, these solutions have had limited success. For the mostpart, these solutions are unnecessarily complicated and expensivebecause they focus on streamlining the data transmission process withthe use of higher capability equipment, or a plurality of remotelylocated video servers.

What is needed is a method for supplying video on demand to a largenumber of subscribers, each of which may request a different program andat times asynchronous to one another. The present invention satisfiesthat need.

SUMMARY OF THE INVENTION

In summary, the present invention describes a system and method in whichan integrated receiver/decoder (IRD) or similar device is used to selectand store programs to support video on demand. In one embodiment,programs are selected by use of a broadcaster-controlled attribute, suchas a flag in a program guide. In another embodiment, this isaccomplished by a customer setup profile (e.g. programs with DOLBYdigital or programs of a specific genre). The IRD scans the programguide to identify VOD candidates, and based on the start times in theprogram guides and transport streams, then schedules the pre-recordingof segments of the identified programs.

The scheduled pre-recording of segments of the identified programs canoccur at a rate that is faster than real time. To accomplish this, theIRD scans the program guide and learns the start time for each of theNVOD candidates. When multiple staggered program start times are found,the IRD determines which portions of the program can be received andstored in parallel in order to pre-record all relevant program segmentsin the shortest time. IRDs with single tuners acquire staggered starttimes that are on the same transport stream, while multi-tuner IRDs cancollect data from many transport streams. After the storage process iscomplete, the customer is informed (for example, by the program guide),that the video program is available for VOD playback.

Once the user demands VOD playback, the pre-stored video segment isplayed back to the user, while the remaining subsequent segments of thevideo program are received and recorded in parallel. These subsequentsegments are spliced to the pre-stored segment and to each other to givethe appearance of VOD playback. In one embodiment, the IRD acquires andstores a purchase information packet (PIP) for each program segment.Further, where program is stored as multiple segments, MPEG dataembedded in the SMPTE time code or the presentation time stampinformation allows the IRD to perform MPEG on line editing to reassemblethe program into a single filestream. The timecode information alsoallows the IRD to acquire and store a video program withoutinterruption. The SMPTE timecode also allows the IRD to store a videoprogram with user interruptions. When the IRD is in the process ofstoring video information to a disk and the customer uses the IRD toview a different program, the IRD can later resume acquisition using alater rebroadcast of the same program to resume the storage at the pointbefore it was interrupted by the user.

In one embodiment, the time-staggered versions of selected (e.g. PPV)video programs are transmitted on channels that are broadcast on acommon transponder. This allows a single-tuner IRD to acquire and storeseveral program segments in parallel, resulting in faster than real timestorage of the subsequent segments of video program while the customeris viewing the pre-stored program segment. So configured, the IRD canreceive and store a video program 2-5 times faster than real time. Thisallows the user to fast-forward anywhere in the program within a singlerebroadcast interval.

Decryption of the pre-stored program segments and the subsequent programsegments is also be performed by the IRD. Since program segments arepre-stored by the IRD in anticipation of customer demand and the storageof the pre-stored segments may be autonomously performed by the IRD, thebroadcaster may not be aware of which program segments were stored byeach customer's IRD. In one embodiment, the IRD solves this problem bystoring conditional access information such as a purchase informationparcel (PIP) with each stored program segment. When the user makes a VODdemand, a message is sent from the IRD identifying each of thesubsequent segments of the video program. In response, the IRD receivesthe PIPs corresponding to the subsequent program segments, and decodes,and splices them together as required. To prevent the customer frombeing billed for multiple viewing of the same program, a modifiedbilling system recognizes that the program segments sent to thecustomer's IRD were part of a VOD program, and would bill the customerfor a single viewing of all of the video segments. In one embodiment,separate PIPs for VOD service are defined, each of which having a valuewhich is an appropriate (e.g. pro-rated according to the time length ofthe segment) fraction of the total charge for the complete programdefined. In another embodiment, the billing system recognizes the PIPsas associated with program segments which were broadcast simultaneously,and adjusts the bill for a single viewing accordingly.

One embodiment of the present invention is described as a methodcomprising the steps of selecting at least one of a plurality of videoprograms for VOD service; receiving and storing a first segment of theselected video program in a local storage device before accepting a userdemand to view the selected video program, wherein the temporal lengthof the first segment is at least substantially equivalent to aretransmission interval; and, after accepting the user demand to viewthe selected video program, retrieving the stored first segment forpresentation while receiving and storing subsequent segments of thevideo program from each of the plurality of channels transmitting aportion of the selected video program in parallel.

One embodiment of the present invention is described by a method ofstoring or viewing a video program in response to a user demand, whereinthe video program is repeatedly transmitted on one of a plurality ofchannels, each repeated transmission separated in time from a precedingtransmission of the video program by a retransmission interval and beingtransmitted on a different channel than the previous transmission. Themethod comprises the steps of selecting at least one of a plurality ofvideo programs, and receiving a plurality of time segments of theselected video program in parallel, wherein each of the time segments isreceived on a different one of the channels.

Another embodiment of the present invention is described by an apparatuscomprising an input device for accepting a selection of at least one ofa plurality of video programs for VOD service; a tuner for receivingmultiple segments of the selected video program in parallel, whereineach segment is received on one of a plurality of channels; and astorage device, for pre-storing a first segment of the selected videoprogram and for storing subsequent segments of the selected videoprogram in parallel while retrieving the pre-stored first segment of theselected video program.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a diagram showing an overview of a video distribution system;

FIG. 2 is a block diagram of an integrated receiver/decoder forpracticing the present invention;

FIG. 3 is a block diagram showing a typical uplink configuration showinghow video program material is uplinked to a satellite for transmissionto subscribers using a single transponder;

FIG. 4A is a diagram of a representative data stream received from asatellite;

FIG. 4B is a diagram illustrating the structure of a data packet;

FIG. 5 is a block diagram illustrating transport module functions;

FIG. 6 is a diagram illustrating the transmission of a video program toprovide near video on demand (NVOD) service;

FIGS. 7A and 7B are flow charts presenting exemplary method steps usedto practice one embodiment of the present invention;

FIG. 8A is a diagram illustrating aspects of the operation of thepresent invention;

FIG. 8B is a diagram showing additional detail regarding the splicing ofprogram material;

FIG. 8C is a diagram showing additional detail regarding caching ofprogram material;

FIG. 9 is a flow chart illustrating exemplary operations used to selectat least one of the plurality of video programs for VOD service; and

FIG. 10 is a diagram illustrating exemplary operations used to selectone of the plurality of video programs for VOD service in anotherembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which form a part hereof, and which show, by way ofillustration, several embodiments of the present invention. It isunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

FIG. 1 is a diagram illustrating an overview of a video distributionsystem 100. The video distribution system 100 comprises a control center102 in communication with an uplink center 104 via a ground link 114 andwith a subscriber 110 via a public switched telephone network (PSTN) orother link 120. The control center 102 provides program material to theuplink center 104, coordinates with the subscribers 110 to offerpay-per-view (PPV) program services, including billing and associateddecryption of video programs.

The uplink center receives program material and program controlinformation from the control center 102, and using an uplink antenna106, transmits the program material and program control information tothe satellite 108. The satellite receives and processes thisinformation, and transmits the video programs and control information tothe subscriber via downlink 118. The subscriber 110 receives thisinformation using the subscriber antenna 112.

In one embodiment, the subscriber antenna 112 is an 18-inch slightlyoval-shaped Ku-band antenna. The slight oval shape is due to the 22.5degree offset feed of the LNB (low noise block converter) which is usedto receive signals reflected from the subscriber antenna 112. The offsetfeed positions the LNB out of the way so it does not block any surfacearea of the antenna 112 minimizing attenuation of the incoming microwavesignal.

The video distribution system 100 can comprise a plurality of satellites108 in order to provide wider terrestrial coverage, to provideadditional channels, or to provide additional bandwidth per channel. Inone embodiment of the invention, each satellite comprises 16transponders to receive and transmit program material and other controldata from the uplink center 104 and provide it to the subscribers 110.However, using data compression and multiplexing techniques the channelcapabilities are far greater. For example, two-satellites 108 workingtogether can receive and broadcast over 150 conventional (non-HDTV)audio and video channels via 32 transponders.

While the invention disclosed herein will be described with reference toa satellite based video distribution system 100, the present inventionmay also be practiced with terrestrial-based transmission of programinformation, whether by broadcasting means, cable, or other means.Further, the different functions collectively allocated among thecontrol center 102 and the uplink center 104 as described above can bereallocated as desired without departing from the intended scope of thepresent invention.

Although the foregoing has been described with respect to an embodimentin which the program material delivered to the subscriber is video (andaudio) program material such as a movie, the foregoing method can beused to deliver program material comprising purely audio information aswell.

FIG. 2 is a block diagram of an integrated receiver/decoder (IRD) 200(also hereinafter alternatively referred to as receiver 200). Thereceiver 200 comprises a tuner/demodulator 204 communicatively coupledto the LNB 202. The LNB 202 converts the 12.2- to 12.7 GHz downlink 118signal from the satellites 108 to, e.g., a 950-1450 MHz signal requiredby the receiver's 200 tuner/demodulator 204. The LNB 202 may provideeither a dual or a single output. The single-output LNB 202 has only oneRF connector, while the dual output LNB 202 has two RF output connectorsand can be used to feed a second receiver or some other form ofdistribution system.

The tuner/demodulator 204 isolates a single, digitally modulated 24 MHztransponder, and converts the modulated data to a digital data stream.The digital data stream is then supplied to a forward error correction(FEC) decoder 206. This allows the receiver 200 to reassemble the datatransmitted by the uplink center 104 (which applied the forward errorcorrection to the desired signal before transmission to the subscriber110) verify that the correct data signal was received, and correcterrors, if any. The error-corrected data may be fed from the FEC decodermodule 206 to the transport module via an 8-bit parallel interface.

The transport module 208 performs many of the data processing functionsperformed by the receiver 200. The transport module 208 processes datareceived from the FEC decoder module 206 and provides the processed datato the video MPEG decoder 214 and the audio MPEG decoder 216. In oneembodiment of the present invention, the transport module, video MPEGdecoder and audio MPEG decoder are all implemented on integratedcircuits. This design promotes both space and power efficiency, andincreases the security of the functions performed within the transportmodule 208. The transport module 208 also provides a passage forcommunications between the microcontroller 210 and the video and audioMPEG decoders 214, 216. As set forth more fully hereinafter, thetransport module also works with the access card 212 to determinewhether the subscriber 110 is permitted to access certain programmaterial. Data from the transport module can also be supplied toexternal communication module 226. The operations performed by thetransport module are further illustrated and described with respect toFIG. 3.

The access card 212 functions in association with other elements todecode an encrypted signal from the transport module 208. The accesscard 212 may also be used for tracking and billing these services. Inone embodiment of the present invention, the access card is a smartcard, having contacts cooperatively interacting with contacts in thereceiver 200 to pass information. In order to implement the processingperformed in the access card 212, the receiver 200, and specifically thetransport module 208 provides a clock signal to the access card 212.

Video data is processed by the MPEG video decoder 214. Using the videorandom access memory (RAM) 236, the MPEG video decoder 214 decodes thecompressed video data and sends it to an encoder or video processor 216,which converts the digital video information received from the videoMPEG module 214 into an output signal usable by a display or otheroutput device. By way of example, processor 216 may comprise a NationalTV Standards Committee (NTSC) or Advanced Television Systems Committee(ATSC) encoder. In one embodiment of the invention both S-Video andordinary video (NTSC or ATSC) signals are provided. Other outputs mayalso be utilized, and are advantageous if ATSC high definitionprogramming is processed.

Audio data is likewise decoded by the MPEG audio decoder 216. Thedecoded audio data may then be sent to a digital to analog (D/A)converter 218. In one embodiment of the present invention, the D/Aconverter 218 is a dual D/A converter, one for the right and leftchannels. If desired, additional channels can be added for use insurround sound processing or secondary audio programs (SAPs). In oneembodiment of the invention, the dual D/A converter 218 itself separatesthe left and right channel information, as well as any additionalchannel information. Other audio formats may similarly be supported. Forexample multi-channel digital audio formats, such as DOLBY DIGITAL AC-3.

A description of the processes performed in the encoding and decoding ofvideo streams, particularly with respect to MPEG and JPEGencoding/decoding, can be found in Chapter 8 of “Digital TelevisionFundamentals, by Michael Robin and Michel Poulin, McGraw-Hill, 1998,which is hereby incorporated by reference herein.

Microcontroller 210 receives and processes command signals from theremote control 224, a receiver 200 keyboard interface, and/or anotherinput device. The microcontroller receives commands for performing itsoperations from a processor programming memory, which permanently storessuch instructions for performing such commands. The processorprogramming memory may comprise a read only memory (ROM) 238, anelectrically erasable programmable read only memory (EEPROM) or, similarmemory device. The microcontroller 210 also controls the other digitaldevices of the receiver 200 via address and data lines (denoted “A” and“D” respectively, in FIG. 2).

The modem 240 connects to the customer's phone line via the PSTN port120. It calls e.g. the program provider and transmits the customer'sprogram purchases for billing purposes, and/or other information. Themodem 240 is controlled by the microprocessor 210. The modem 240 canoutput data to other I/O port types including standard parallel andserial computer I/O ports.

The present invention also comprises a local storage unit such as thevideo storage device 232 for storing video and/or audio data obtainedfrom the transport module 208. Video storage device 232 can be a harddisk drive, a read/writable compact disc of DVD, a solid state RAM, orany other storage medium. In one embodiment of the present invention,the video storage device 232 is a hard disk drive with specializedparallel read/write capability so that data may be read from the videostorage device 232 and written to the device 232 at the same time. Toaccomplish this feat, additional buffer memory accessible by the videostorage 232 or its controller may be used. Optionally, a video storageprocessor 230 can be used to manage the storage and retrieval of thevideo data from the video storage device 232. The video storageprocessor 230 may also comprise memory for buffering data passing intoand out of the video storage device 232. Alternatively or in combinationwith the foregoing, a plurality of video storage devices 232 can beused. Also alternatively or in combination with the foregoing, themicrocontroller 210 can also perform the operations required to storeand or retrieve video and other data in the video storage device 232.

The video processing module 216 output can be directly supplied as avideo output to a viewing device such as a video or computer monitor. Inaddition the video and/or audio outputs can be supplied to an RFmodulator 234 to produce an RF output and/or 8 vestigal side band (VSB)suitable as an input signal to a conventional television tuner. Thisallows the receiver 200 to operate with televisions without a videooutput.

Each of the satellites 108 comprises a transponder, which acceptsprogram information from the uplink center 104, and relays thisinformation to the subscriber 110. Known multiplexing techniques areused so that multiple channels can be provided to the user. Thesemultiplexing techniques include, by way of example, various statisticalor other time domain multiplexing techniques and polarizationmultiplexing. In one embodiment of the invention, a single transponderoperating at a single frequency band carries a plurality of channelsidentified by respective service channel identification (SCID).

Preferably, the receiver 200 also receives and stores a program guide ina memory available to the microcontroller 210. Typically, the programguide is received in one or more data packets in the data stream fromthe satellite 108. The program guide can be accessed and searched by theexecution of suitable operation steps implemented by the microcontroller210 and stored in the processor ROM 238. The program guide may includedata to map the channel numbers to satellite transponders and servicechannel identifications (SCIDs), and also provide TV program listinginformation to the subscriber_identifying program events.

FIG. 3 is a block diagram showing a typical uplink configuration for asingle satellite 108 transponder, showing how video program material isuplinked to the satellite 108 by the control center 102 and the uplinkcenter 104. FIG. 3 shows three video channels (which could be augmentedrespectively with one or more audio channels for high fidelity music,soundtrack information, or a secondary audio program for transmittingforeign languages), and a data channel from a computer data source 306.

The video channels are provided by a program source of video material300A-300C (collectively referred to hereinafter as video source(s) 300).The data from each video program source 300 is provided to an encoder302A-302C (collectively referred to hereinafter as encoder(s) 302). Eachof the encoders accepts a program time stamp (PTS) from the controller316. The PTS is a wrap-around binary time stamp that is used to assurethat the video information is properly synchronized with the audioinformation after encoding and decoding. A PTS time stamp is sent witheach I-frame of the MPEG encoded data.

In one embodiment of the present invention, each encoder 302 is a secondgeneration Motion Picture Experts Group (MPEG-2) encoder, but otherdecoders implementing other coding techniques can be used as well. Thedata channel can be subjected to a similar compression scheme by anencoder (not shown), but such compression is usually either unnecessary,or performed by computer programs in the computer data source (forexample, photographic data is typically compressed into *.TIF files or*.JPG files before transmission). After encoding by the encoders 302,the signals are converted into data packets by a packetizer 304A-304F(collectively referred to hereinafter as packetizer(s) 304) associatedwith each source 300.

The data packets are assembled using a reference from the system clock314 (SCR), and from the conditional access manager 308, which providesthe SCID to the packetizers 304 for use in generating the data packets.These data packets are then multiplexed into serial data andtransmitted.

FIG. 4A is a diagram of a representative data stream. The first packetsegment 402 comprises information from video channel 1 (data comingfrom, for example, the first video program source 300A). The next packetsegment 404 comprises computer data 0nformation that was obtained, forexample from the computer data source 306. The next packet segment 406comprises information from video channel 5 (from one of the videoprogram sources 300), and the next packet segment includes informationfrom video channel 1 (again, coming from the first video program source300A). The data stream therefore comprises a series of packets from anyone of the data sources in an order determined by the controller 316.The data stream is encrypted by the encryption module 318, modulated bythe modulator 320 (typically using a QPSK modulation scheme), andprovided to the transmitter 322, which broadcasts the modulated datastream on a frequency bandwidth to the satellite via the antenna 106.The receiver 200 receives these signals, and using the SCID, reassemblesthe packets to regenerate the program material for each of the channels.As shown in FIG. 4A, null packets created by the null packet module 312may be inserted into the data stream as desired.

FIG. 4B is a diagram of a data packet. Each data packet (e.g. 402-416)is 147 bytes long, and comprises a number of packet segments. The firstpacket segment 420 comprises two bytes of information containing theSCID and flags. The SCID is a unique 12-bit number that uniquelyidentifies the data packet's data channel. The flags include 4 bits thatare used to control whether the packet is encrypted, and what key mustbe used to decrypt the packet. The second packet segment 422 is made upof a 4-bit packet type indicator and a 4-bit continuity counter. Thepacket type identifies the packet as one of the four data types (video,audio, data, or null). When combined with the SCID, the packet typedetermines how the data packet will be used. The continuity counterincrements once for each packet type and SCID. The next packet segment424 comprises 127 bytes of payload data, which is a portion of the videoprogram provided by the video program source 300. The final packetsegment 426 is data required to perform forward error correction.

FIG. 5 is a block diagram showing additional detail regarding theoperations of the transport module. The data packets which are received,demodulated, synchronized and reverse FEC coded from the FEC module 206are provided to a demultiplexer such as the SCID select module 502.Program selection information is processed by the microcontroller 210,and used to select the one or more SCIDS associated with the desiredprogram (a program may be separated into several streams, each with anassociated SCID). As set forth more fully herein, program selection caninclude a selection for ordinary viewing, or for VOD recording. Inaddition, the selection of a program for VOD recording can beaccomplished by the subscriber, according to an express selection, aresult of a processing routine to predict the subscribers preferencesfrom a viewing history, or by selection by the control center 102.

The SCID select module compares the selected SCID or SCIDs with theSCIDs for the incoming packets, and passes those packets with SCIDsmatching the selected channel(s). For single channel service,non-selected packets (packets without the subscriber-selected SCID) aresimply discarded.

In the typical case where a video program comprises multiple streamelements, the SCID select module passes the required packets. If morethan one channel is desired (e.g. to allow the reception and recordingmultiple channels at a time while simultaneously viewing them) the SCIDselect module 502 passes these the stream elements for the additionalchannels as well.

In the preferred embodiment, all program material is encrypted. Forviewing encrypted programming, the receiver 200 is responsible forverifying that access should be granted, and if so, decrypting the datapackets so the program material can be viewed by the subscriber. Forunencrypted programming, the data router 514 directs the data packetsdirectly in the system RAM 228 via DMA 508.

To provide program information for use in the distribution and viewingof PPV program material, the control center 102 transmits (via theuplink center 104 and the satellite 108) a purchase information packet(PIP) that is associated with PPV program materials described in theprogram information guide. When the subscriber wants to view PPV programmaterial, the receiver 200 is used to select the corresponding PPVprogram material. The receiver obtains a PIP pointer, and tunes to atransponder that carries the PIP. A PIP pointer is a numerical valuethat is stored with a program in the program guide stream orfunctionally computed from a program's channel and start time (e.g. PIPpointer=program.PIP_pointer, or PIP pointer=f(channel, start time)). ThePIP is received by the receiver 200 by acquiring the PIP for the sendPIP pointer, and provided to the access card 212, which checks the PIPfor purchasability (e.g. blackouts, rating, credit balance, etc.).

Each data packet is associated with a control word packet (CWP) that isreceived by the transport module 208. The CWP encodes each program toprevent tampering, and is used to generate a CW and a CW status, whichare stored in the CW memory 504. The CW is used to enable data packetsto be retrieved from the system RAM 228 and provided to the video MPEGdecoder 214 and/or audio MPEG decoder 216, and may also be used todecrypt the data packet itself.

As set forth more fully below, the present invention also providesnon-real time viewing capability to the viewer. This non-real timeviewing capability includes (1) the ability to store a video program inits entirety for complete off-line viewing at a later date, and (2) theability to “pre-store” the first portion of a video program to providevirtual VOD service. In case (2), an initial segment of the videoprogram is recorded in advance of the user request (e.g., the first 30minutes). When the user decides to view the video program, the“pre-stored” segment is played back, while the subsequent remainingvideo program segments (which are each transmitted on differentchannels) are recorded. These segments are spliced together to provide avirtual video on demand system that provides the appearance of truevideo on demand.

Programs eligible for VOD service may be indicated as such by the VODindicator or other appropriate flag in the program guide or other dataservice. Eligibility may also be determined by analysis of theavailability alternate program information start times and determiningif the alternate program start times will support VOD service. In oneembodiment, the IRD determines VOD service availability using staggeredshowings of the same program by use of information in the program guide.The program guide supplies the channel number and start time of allprogram material. The IRD can use the staggered showing information torecord the program material at a rate faster than real time.

Programs that are eligible for VOD service may include encrypted PPVprograms, encrypted non-PPV programs, and non-encrypted programs.

The storage of non-encrypted data segments is accomplished by passingthe data through the system RAM 228 (indicated by the first switch 514in the up position) and then to the video storage device 232, or bypassing the data directly from the transport module 208.

The retrieval of non-encrypted data segments is accomplished by readingthe data segments from the video storage device 232 and routing thosedata segments to the system RAM 228 using the data router 514 and theDMA to system RAM 508, where they can be read and provided to the MPEGdecoders 214, 216.

The storage of encrypted data packets can be accomplished in one of twoways. First, the encrypted data packets can be decrypted by thedecryption module 506 as described above, and passed through the systemRAM 228 to the video storage device 232. This method is appropriate, forexample, when the subscriber 110 is entitled to view all encryptedprogram material (e.g. a monthly subscription). Alternatively, thereceiver 200 can store the data packets in encrypted form and decryptthem for later viewing after a purchase choice is made by the customer.In one embodiment data router 514 directs encrypted data segmentsdirectly to the video storage device 232. In another embodiment, theencrypted data is sent to the video storage device 232 via the systemRAM 228.

Two levels of encryption can also be used to implement an additionallayer of access control for PPV programs. A first level of accesscontrol can be used to limit access to persons who are authorized topurchase a PPV program (e.g. subscribers) and the second level of accesscontrol can be used to limit access to the PPV program to those who haveactually purchased a PPV program. In this case, data packets may bedecrypted to the first level of access, and stored in the video storagedevice 232. However, since the data packets are encrypted according totwo levels of access control, the data must be read from the videostorage device 232 and decrypted to the second level of access beforethe video data can be decoded and presented to the user.

In either case, the encrypted data packets must be decrypted beforepresentation to the user. This is accomplished by reading the encrypteddata packets from the video storage device 232, and routing thesepackets to the decrypt module 506. These encrypted data packets are thendecrypted and stored in the system RAM 228 for DMA access by the MPEGdecoders 214, 216.

In one embodiment, the decryption process is accomplished as follows. Inresponse to a user demand and while retrieving the stored first segment804 for presentation to the user, a message is transmitted from the IRD200 separately identifying each of the subsequent segments 806 of theselected video program and the user to the program source such as thecontrol center 102 or the uplink center 104. A code or key such as thePIP is then received by the IRD 200. The key is later used to decryptthe encrypted segments so the video program can be viewed by the user.

In another embodiment, a message is transmitted to the IRD 200separately identifying each of the subsequent segments 806 of theselected video program and the user to the program source such as thecontrol center 102 or the uplink center 104. In response, a plurality ofcodes or keys are transmitted and received by the IRD 200, and each ofthe keys is used to decrypt an associated one of the encryptedsubsequent segments 806.

FIG. 6 is a diagram illustrating the transmission of a video program toprovide near video on demand (NVOD service). NVOD service isaccomplished by broadcasting the same video program 602 on a pluralityof program channels with each channel temporally separated by arebroadcast interval 604. As shown in FIG. 6, the video program can bebroadcast at 5:00 on channel 1 (using the appropriate SCID), 5:30 onchannel 2, 6:30 on channel 3, and so on. Using this broadcast technique,the video program can be viewed from the beginning to the end, withoutrequiring the user to wait for more than 30 minutes (hence, providingnear video on demand). As shown in FIG. 6, this means that at anyparticular time, during an time interval 606, different time segments ofthe video program 608A-608E (hereinafter referred to collectively assegments 608) are broadcast in parallel, and can be received by thereceiver 200.

FIGS. 7A and 7B describe a flow chart presenting exemplary method stepsused to practice one embodiment of the present invention. First, asshown in FIG. 7A, at least one of a plurality of video programs isselected 702 for video service. The point in time at which the pluralityof video programs was selected for VOD service is indicated as t_(s)802. A first segment of the selected video program is then received andstored. This is illustrated in block 704 of FIG. 7A and by the“pre-store” interval 804 extending from time t_(p1) to time t_(p2) inFIG. 8A. Typically, the time length of the pre-stored video programmaterial segment 804 is equal to the rebroadcast interval t_(R) 604.This allows all of the subsequent time segments 806A-806D (collectivelyreferred to hereinafter as subsequent time segment(s) 806) of the videoprogram to be recorded while the pre-stored video program segment 804 isplayed back for viewing. However, the length of the pre-stored videoprogram material segment can be greater than the rebroadcast interval604, to provide additional video program material for use in splicingthe subsequent segments 806 to the pre-stored segment 804, or to provideadditional time for the splicing process to be completed.

Returning to FIG. 7A, when the user requests 706 VOD service, thepre-stored segment 804 is retrieved for presentation to the subscriber110. While this retrieval is taking place, the subsequent segments 806of the video program material are being received from some of theplurality of channels (channels 3, 4, 5, and 6 in FIG. 8A, for example)are received and stored in the video storage device 232. The foregoingoperations occur in parallel so that the data from all of the relevantchannels can be received and stored while retrieving the stored firstsegment for presentation to the subscriber 110. If necessary, this canbe implemented with separate disk drives or memories for fasterprocessing.

As shown in FIG. 8A, depending on the time the subscriber demands VODservice t_(D), data present on some of the channels need not berecorded. For example, given the demand time t_(D) shown in FIG. 8A, thefirst portion of the program information on channel 6 need not berecorded, since it is duplicative of the information in the pre-storedsegment 804 being retrieved from the storage device 232. Instead, theonly program information that must be recorded is the last t_(R)-(t_(D)-t_(A)) portion of the video segment, wherein t_(A) is thecommencement time for the most recent broadcast of the program, andt_(R) is the rebroadcast interval. The interval of the subsequent videoprogram segment 806D that must be recorded is shown as interval 808. Theremainder of the interval of the subsequent video program segment 806need not be recorded, and the bandwidth normally used for receiving andstoring this information can be directed to other purposes (e.g. storingother program material for VOD service).

Turning to FIG. 7B, the subsequent segments 806 are spliced to thepre-stored segment 804 using the techniques set forth herein. In oneembodiment, the splicing of segments is prioritized according to pointin the video program currently selected by the user. If the user isviewing the video program from start to end, without interruption, fastforward, or rewind, the end of the pre-stored segment 804 is spliced tothe beginning of subsequent segment 806D first, and then the beginningof each subsequent segment is spliced to the end of the precedingsubsequent segment (hence, after splicing, the order of the segments ispre-stored segment 804, subsequent segment 806D, subsequent segment806C, etc.).

In one embodiment of the present invention, the user cannot fast forwardpast the pre-cached segment 804 until the immediately following segment(i.e. segment 806D) has been recorded. Hence, the VOD system allows anasynchronous start of viewing, but truly random access to all programmaterial is only available after all of the program segments 806A-806Dhave been recorded.

However, since the multi-channel reception and storage described hereinpermits the remainder of the program material to be downloaded rapidly,another embodiment of the present invention permits the subscriber 110to fast forward and rewind while viewing the retrieved pre-storedsegment 804 and storing the subsequent segments 806. In such cases,different splicing techniques are implemented. For example, if the useris in the middle of viewing the pre-stored segment 804 and issues acommand to fast forward the program to a time near the beginning of thelast subsequent segment of the program 806A, the splicing of subsequentsegment 806B to subsequent segment 806A will be granted a higherpriority than the splicing of pre-stored segment 804 to the firstsubsequent segment 806D. It should also be noted that to further improveperformance, data from the end of the pre-stored segment 804 may beretrieved in parallel with other data being retrieved from thepre-stored segment 804 for subscriber viewing to allow essentially“pre-splice” the end of the pre-stored segment 804 to the beginning ofthe (recently received) subsequent segment 806D.

It should also be noted that the splicing between the pre-stored segment804 the first subsequent segment 806D can be performed at differenttimes, which can be advantageously chosen to minimize the splicing timeor to maximize fast-forward and rewinding capability.

FIG. 8B is a diagram illustrating the different times that thepre-stored segment 804 may be spliced to the first subsequent segment806D. By inspection, the first time at which a splice may be performedbetween pre-stored segment 804 and the subsequent segment 806D is a timet_(SP1), and the last time a splice may be performed is at time t_(SP2).The actual splicing time can be determined according to a number of userinput or program parameters. For example, the selection of a splice timeof t_(SP2) permits the user to fast-forward, reverse, and pause anywherewithin the pre-stored segment 804 at will with minimum programinterruption. Conversely, the selection of splice time t_(SP2) minimizesmemory requirements, as less program material need be stored to provideVOD service. Conversely, if the splice time t_(SP1) is selected, segment806D need not be stored at all, as the pre-stored segment 804 may bespliced to the broadcast program material as soon as practicable. Thiseffectively minimizes memory and throughput requirements. Further, iftime segment information is provided in the program material, fastforward and reverse operations may be implemented by splicing back topre-stored segment 804 program material as required.

FIG. 8C is a diagram showing additional detail regarding the caching andsplicing of program material. In the illustrated case, a program “A” is125 minutes long, and the rebroadcast interval is 125 minutes. Hence,the program includes four thirty-minute segments 810B-810E and afive-minute segment 810A. The IRD 200 pre-stores a first segment 804having 30 minutes of program material in anticipation of a customer'sdesire to view program “A.” This can occur, for example in the intervalbetween 6:30 and 7:00 as depicted in FIG. 8A. The PIP is also pre-storedor cached if the program is a PPV program. Audio tracks can be recordedalong with the video information. These audio tracks can include allaudio tracks, or only one or more preferred audio tracks (i.e. audiotracks corresponding to a particular language or program rating).

After the customer requests viewing of the program material at timet_(D), the IRD 200 begins playing back the pre-recorded segment 804, andsearches the program guide for staggered showings of program “A”. TheIRD 200 then begins to record the available program segments 810A-810Dfrom the staggered showings of program “A” while playing back theprerecorded segment 804. After an amount of time elapses, a viewedportion 812 t_(V) of the pre-recorded segment 804 has been played backand portions 814A-814D of the remaining segments 810A-810D are recorded.As time passes, the viewed portion 812 t_(V) gets larger, as do therecorded portions 814A-814D or the remaining segments 810A-810D. Forexample, in the fourth illustration from the top of FIG. 8C, twenty-nineminutes of the prerecorded interval 812 have been played back, with 1minute of anticipated pre-recorded storage material 820 remaining, andthe IRD has completed caching 29 minutes of each 30 minute programsegment, as illustrated in elements 814A-814D. A total of three minutesof program material remains to be recorded (one minute from each of theprogram segments). These remaining portions are illustrated in FIG. 8Cas 824B-824D. By the time the end of the pre-recorded segment 804 isreached, all of the remaining segments 810A-810D have been recorded. Atthis time, the program material at the end of segment 812 is spliced tothe program material beginning at 814D. Similarly, the program materialat the beginning of each segment 814A-814C is spliced to the end of theprogram material of the preceding program segment. In one embodiment,the program material at the end of the pre-recorded segment 812 isspliced to the program material in the following program segment 814Dbefore the playback of the pre-recorded segment 812 is completed. Sincethe material at the beginning of the following program segment 814D isavailable soon after the viewer begins playing back the pre-recordedsegment, the information required to perform the necessary splicingoperations is available before all of the program material in theprerecorded segment 812 has been played back, and before all of theprogram material of the following segment 814D has been recorded. Hence,the segments may be pre-spliced if necessary.

In a preferred embodiment of the present invention, the IRD 200 includesa single tuner/demodulator 204 and associated circuitry which canreceive and decode all the necessary channels for VOD service (e.g.channels 3-6 in FIG. 8A) from the same frequency band, and is able tosimultaneously acquire and handle bandwidth from Z program streamswherein Z is defined as:

$Z = {{ceiling}\left( \frac{X}{t_{R}} \right)}$

wherein X is the duration of the program in minutes, and t_(R) is theamount of pre-cached material in minutes. Hence, in the foregoingexample,

$Z = {{{ceiling}\left( \frac{125}{30} \right)} = {{{ceiling}(4.1667)} = 5.}}$

When one segment is pre-cached, the IRD 200 need only cache theremaining segments. Thus, in this case,

$Z = {{{ceiling}\left( \frac{X}{t_{R}} \right)} - 1}$

If an IRD 200 with a single tuner/demodulator 204 cannot accommodate thesimultaneous reception and storage of Z program streams, then the IRD200 may not be able to cache the entire program in the time it takes toplay back the initially cached program segment. In this case, the singletuner IRD 200 may give precedence to the earliest segments (e.g. 806Dand perhaps 806C) and later record the remaining, yet unrecorded programsegments (e.g. segments 806B and 806A).

Alternate embodiments using IRDs 200 with two or more tuner/demodulators204 are possible as well. Generally, IRDs 200 with multiple tuners(n-tuner IRDs 200) can be used to receive staggered shows on n-frequencybands. For example, the time-staggered video programs may be broadcaston two frequency bands, and received by an IRD 200 having twotuner/demodulators 204, one tuner/demodulator 204 for receiving signalson each of the two frequency bands. Further, it is possible to broadcastm time-staggered video programs on n frequency bands. In thisembodiment, IRDs 200 with single tuner/demodulator 204 can receive asubset of the m video programs (the time-staggered video programsbroadcast on one of the n frequency bands), while IRDs 200 with multipletuner/demodulators 204 can receive additional video programs as well.

Hence, 2-tuner or more (n-tuner) IRDs 200 can be used to eliminate thelimitation on the broadcaster for all staggered start time transmissionsof a program to be all on the same frequency.

N-tuner IRDs 200 can also be used to reduce storage requirements aswell. Since the N-tuner IRD can be used to receive more information in agiven amount of time, the IRD 200 need pre-store much less information,allowing the user to pre-store data for more video programs in the videostore 232. For example, an IRD 200 with a single tuner/demodulator 204can be used to receive the channels 2-6 shown in FIG. 8A. An IRD 200with two tuner/demodulators 204 can be used to receive additionalmaterial broadcast on a channel 3A (staggered in time from channel 3 by15 minutes), channel 4A (staggered in time from channel 4 by 15minutes), and channel 5A (staggered in time from channel 5 by 15minutes). For such an IRD 200, the rebroadcast interval is effectivelyreduced to 15 minutes, and the IRD 200 need only pre-store 15 minutesworth of program material (allowing either more pre-cached programmaterial or relaxed storage requirements), instead of the 30 minutes ofprogram material required by the single-tuner/demodulator 204 IRD 200.Advantageously, this additional capability does not render the singletuner/demodulator 204 IRD 200 obsolete. As can be seen from theforegoing, additional IRD 200 video store 232 memory permits a reducedrebroadcast interval as well. The foregoing can also be used to downloadand cache the entire program more quickly, thus allowing random programaccess (through fast-forward and reverse operations, for example) morerapidly.

Several alternatives are available to splice MPEG-coded data together.If the splices are infrequent (i.e. at the start of the video program),the data stream can be abruptly switched from the pre-stored videoprogram segment 804 to the next subsequent video program segment 806D.In this case, the MPEG decoders 214 216 will have to reacquire lock onthe program material. This may result in a disruption in the programmaterial of at least 1 group of pictures (GOP) in length, which wouldappear similar to a change of channel.

In another embodiment of the present invention, dual MPEG decoder pairs214 and 216 (two video MPEG decoders 214 and two audio MPEG decoders216) are used. This can be implemented with a transport module 208 andMPEG decoder pair 214, 216 for the current segment, and a secondtransport module and second MPEG decoder pair for a next subsequentsegment 806D. When the end of the pre-stored video program segment 804is reached, the video signal from the output of the first MPEG decoder214 is simply switched to the second MPEG decoder, eliminating thedisruption described above. The foregoing can also be implemented with asingle transport module, but dual MPEG decoders 214, 216 as well. Asdescribed above, the length of the pre-stored video program segment canbe increased beyond the rebroadcast interval 604 so that the foregoingsplicing problems can be ameliorated. Similarly, the recording intervalof each of the subsequent video program segments 608 can be increasedbeyond the retransmission interval to promote clean splicing from one ofthe subsequent segments to the next. Another method of MPEG splicinginterleaves or otherwise associates each of the video segments 804, 806with a time code such as the SMPTE standard 312M time code. This timecode can then be used to reassemble and splice together the videosegments 804, 806. The proposed SMPTE standard 312M time code isdescribed in the October 1998 issue of the SMPTE Journal, which ishereby incorporated by reference herein.

In addition to the foregoing MPEG splicing, there is also the issue ofsub-segment management. Sub-segment management addresses the difficultyposed by the possibility that data packets (e.g. packets 402-416) willarrive at the transport module 208 (and hence, the demultiplexingelement 502) in sequence, but in uncertain time intervals. Eachsub-segment, which may comprise one or more packets, must be reassembledto produce the program material.

Each sub-segment can be assembled by sorting by a channel identifier(such as the SCID), and the sorting the assembled sub-segments inaccordance with a time code. The SMPTE time code, which is usuallydefined in terms of hours, minutes, and seconds of the program asHH.MM.SS, can be used for this purpose. Alternatively or in combinationwith the foregoing, a recirculating program time stamp (PTS) valuedescribed above can be used for the time stamp. To splice segmentstogether, the last I frame of a previous segment is spliced with thefirst I frame of a subsequent segment. Since the PTS provides anindication of the program time, it can be used to match the I frames sothat the segments may be properly spliced together. Since the PTS is awrap-around binary counter, ambiguities may be encountered. Ifnecessary, a time-of-day clock can be used in conjunction with the PTSto eliminate the ambiguities caused by the wrap-around characteristic.

FIG. 9 is a flow chart illustrating exemplary program steps used toselect at least one of the plurality of video programs for VOD service.As described earlier herein, the receiver 200 stores a program guidewhich presents a description of the video programs available for viewingnow and for a period of time in the future to the viewer. Each of thevideo programs includes a SCID, which identifies that program. Byselecting the SCID, the receiver is set to retrieve the video programsegments associated with the SCID for viewing. An indicator such as aflag, a bit or word can be associated with each video program in theprogram guide for which VOD services are desired. In one embodiment, theindicator may be placed in the program guide by the control center 102before the program guide is downloaded in the receiver 200, eitherthrough the PSTN link 120 or the downlink 118. The program guide is thenscanned 902 to find the VOD service indicator. Video programs associatedwith a VOD service indicator are then identified as programs to berecorded for VOD service, as shown in block 904.

The indicators may also be placed, removed, or altered by the subscriber110 using the keyboard or remote control 224 while viewing the programguide (essentially scanning through the guide and using an appropriateinput to designate the program as a VOD program). In one embodiment, thevideo program provider provides baseline VOD service designations, butthe user can elect to do so as well, with the user's selections givenpriority in the situation where there is inadequate time and/orbandwidth to pre-store all video segments that have been defined. It isalso possible for a program provider VOD selection download to beinterrupted by a user-selected VOD selection, and completed when thechannels are available to do so. The program guide can also includeinformation to augment the designation of a program for VOD service. Forexample, data can be associated with each program indicating when therecording of the pre-stored segment 804 should commence. This allows thevideo provider to efficiently schedule the storing of pre-storedsegments 804 (using information that may include global knowledge of theVOD selections from each subscriber). Hence, the storage of pre-storedsegments 804 can occur in the middle of the night or at some other timewhen there are more channels or more bandwidth available to do so.Similarly, if desired, entire movies can be transmitted over multiplechannels and made available for true VOD service.

FIG. 10 is a diagram illustrating another method of selecting one of theplurality of video programs for VOD service. Here, the subscriber hasnot made any express program selections for VOD service, but has insteadelected to allow the receiver to do so based upon a personalizedindication of which programs the subscriber may want to see. Thispersonalized indication may be obtained from the viewing history of theuser, as sensed and recorded by the receiver 200. Or, the user mayindicate the genre or category of program material that the subscriberprefers. The receiver then uses this information to generate a list ofprograms for which the subscriber will likely want VOD service. The usermay then edit this list to remove uninteresting programs, or simplyallow the receiver to retain those program designations for VOD service.This can be accomplished by accepting a selection of a category of videoprograms for VOD service (e.g. basketball programs, drama, a particularactor or director, designation as including a secondary audio program ina different language), as shown in block 1002. After an appropriatesearch of program information guide information is performed, the VODindictor previously described is associated with each video program thatis a member of the user's category of video programs, as shown in block1004.

In yet another embodiment of the present invention, the IRD 200 iscapable of identifying programs that are available for VOD servicewithout the use of a VOD service indicator. This is accomplished byscanning an electronic program guide accessible to or stored within theIRD 200 to determine instances when the same video program is scheduledto be transmitted on multiple channels at staggered starting intervals.This is accomplished by comparing video program information such as theprogram's title and/or other related attributes such as a unique programidentifier for the programs in the program guide. When the program titleof other information match and the scheduled broadcast time arestaggered so as to virtual VOD service, the IRD 200 schedules multiplesimultaneous recordings to record the required program material(typically, the pre-stored segment 804). This capability can beperformed with or without user intervention.

As described above, the decryption of encrypted data packets requires aPIP, which, along with the CWPs, is used by the access card 212 todecrypt the data packets and to provide DMA access to the decrypted datain the system RAM. For non-real time operations, this can beaccomplished in a number of ways.

In one embodiment of the present invention, the pre-stored video programsegment 804 is transmitted and stored in an unencrypted form and thesubsequent video program segments are transmitted and stored in anencrypted form. This allows the subscriber to store and view pre-storedvideo segment 804 for VOD playback without requiring the PIP, and alsoallows the subscriber to view at least a portion of the pre-stored videosegment before requesting the remainder of the video program. Each ofthe subsequent video program segments 806, however require a PIP, andhence, the remainder of the video program cannot be viewed until thereceiver obtains the required PIPs for the remaining segments of thevideo program. These PIPs can be obtained before VOD service begins, orcan be obtained after the commencement of VOD service.

In one embodiment of the present invention, the retrieval of thepre-stored video program segment 804 can be interrupted (e.g. after 5minutes) and the subscriber 110 queried as to whether they wish topurchase the remainder of the program. If the subscriber 110 so elects,the PIPs can be provided to decrypt and access the remainder of thevideo packets. Since each segment of the video program (806A-806D) isassociated with a different PIP, information at the control center 102can be used to determine which PIPs are required to decrypt the entirevideo program in sequence, and send those PIPs to the subscriber'sreceiver 200.

In another embodiment of the invention, all of the video segments,including the pre-stored video segment 804 and the subsequent videosegments 806 are encrypted. In this case, the PIP for the first videosegment must be obtained before the video segment can be decrypted andplayed back. In one embodiment, the PIP for the first segment isobtained after the subscriber requests VOD service. A message ispresented to the user, giving the price of the VOD program, andconfirming that the subscriber is requesting that service. The controlcenter 102 then makes the PIP for the first video segment available tothe receiver 200 so that the decryption can commence. The control centercan also determine the PIP for the subsequent segments (either alongwith the PIP for the first segment or when the subsequent segments 806are being transmitted), and provide those PIPs to the receiver so thatthe remaining segments can be decrypted.

Conclusion

This concludes the description of the preferred embodiments of thepresent invention. The foregoing description of the preferred embodimentof the invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. For example, asingle demultiplexing element (the SCID selection module 502) can beused to demultiplex the information on multiple video channels ofinterest. The foregoing invention can also be implemented with multipledemultplexing elements or with multiple transport modules 208. Forexample, one demultiplexing element and/or transport module 208 can beprovided for each video channel to be received in parallel. Thisconfiguration substantially speeds up the demultiplexing and decryptingoperations. Further, the foregoing operations can also be performed inmultiple transponder embodiments in which the receiver 200 not only hasa demultiplexer element or transport module 208 for each channel, butalso multiple tuners 204, each for receiving a signal on one of aplurality of transponders providing program material via downlink fromthe satellite 108.

It is also possible to select the length of the pre-store interval 804to be less than the rebroadcast interval 604. In this embodiment,virtual video on demand service cannot be provided to the subscriber 110for any random start time t_(D). However, this method can be used toimprove the near video on demand service (NVOD) to effectively reducethe rebroadcast interval 604. For example, suppose that the actualrebroadcast interval 604 for the video program material is 30 minutes.If only 15 minutes of the program is pre-stored, true video on demandservice for any random start time t_(D) cannot be provided, since all ofthe remaining segments cannot be recorded before the 15 minutepre-stored interval expires. However, if the subscriber is constrainedto begin replaying the stored material in the last 15 minutes of therebroadcast interval, the pre-stored information can be played backwhile the remainder of the program material segments is stored, withoutloss of the program material. Hence, the pre-recorded segment can beused to effectively reduce the latency in the NVOD service by 100%.

It is intended that the scope of the invention be limited not by thisdetailed description, but rather by the claims appended hereto. Theabove specification, examples and data provide a complete description ofthe manufacture and use of the composition of the invention. Since manyembodiments of the invention can be made without departing from thespirit and scope of the invention, the invention resides in the claimshereinafter appended.

1. A method of providing a video program to a user, wherein the videoprogram is repeatedly transmitted on one of a plurality of channels,each repeated transmission temporally separated from a previoustransmission by a retransmission interval and being transmitted on adifferent channel than the previous transmission, the method comprisingthe steps of: receiving and storing a first segment of a selected videoprogram in a local storage device before accepting a user command toview the selected video program, wherein a temporal length of the firstsegment is substantially equivalent to the retransmission interval; andafter accepting the user command to view the selected video program,retrieving the stored first segment for presentation to the user whilereceiving and storing subsequent segments of the video program from atleast one of the plurality of channels transmitting the video program.2. The method of claim 1, further comprising the step of selecting theselected video program from a plurality of video programs for video ondemand (VOD) service.
 3. The method of claim 2, wherein the step ofselecting the selected video program from a plurality of video programsfor VOD service comprises the steps of: scanning a program guide havingan entry for each of the video programs for a VOD service indicator; andidentifying a video program associated with the VOD service indicator asthe selected video program.
 4. The method of claim 3, wherein theprogram guide is stored in the local storage device.
 5. The method ofclaim 3, wherein the step of selecting the selected video program from aplurality of video programs for VOD service comprises the steps of:accepting a selection of at least one of the video programs for VODservice; and associating the VOD indicator with the entry of each videoprogram selected for VOD service.
 6. The method of claim 5, wherein thestep of selecting the selected video program from a plurality of videoprograms for VOD service is performed by the user and the method furthercomprises the step of presenting the program guide to the user.
 7. Themethod of claim 2, wherein the step of selecting the selected videoprogram from a plurality of video programs for VOD service comprises thesteps of: scanning a program guide having an entry for each of theplurality of video programs to identify at least one video programscheduled to be repeatedly transmitted on one of a plurality ofchannels, each repeated transmission temporally separated from aprevious transmission by a retransmission interval and being transmittedon a different channel than the previous transmission; and selecting theidentified video program as the selected video program.
 8. The method ofclaim 7, wherein the step of scanning the program guide comprises thestep of comparing video program information for each of the entries,wherein the video program information comprises a program title.
 9. Themethod of claim 7, wherein the step of scanning the program guidecomprises the step of comparing video program information for each ofthe entries, wherein the video program information comprises a uniqueprogram identifier.
 10. The method of claim 1, wherein the step ofreceiving and storing a first segment of a selected video program in alocal storage device comprises the step of receiving data representingthe first segment of the video program from a program source in areceiver communicatively coupled to the local storage device at a timescheduled by the program source.
 11. The method of claim 1, furthercomprising the step of splicing the subsequent segments to the firstsegment for presentation to the user in response to the user command.12. The method of claim 11, wherein the video segments each comprise aplurality of video sub-segments each sub-segment associated with a timecode, and the step of splicing the subsequent segments to the firstsegment for presentation to the user comprises the step of sorting thesub-segments in accordance with the time codes.
 13. The method of claim12, wherein the time code is an SMPTE time code.
 14. The method of claim12, wherein the time code is a program time stamp.
 15. The method ofclaim 11, wherein the video segments each comprise a plurality of videosub-segments, each sub-segment associated with a time code and a channelidentifier, and the step of splicing the subsequent segments to thefirst segment for presentation to the user comprises the steps of:assembling the sub-segments by the associated channel identifier; andsorting the assembled sub-segments in accordance with the time codes.16. The method of claim 1, wherein each of the subsequent segments isencrypted so as to be decryptable with a key before being received andstored in the local storage device, and the method further comprises thesteps of: in response to the user command and while retrieving thestored first segment for presentation to the user, transmitting amessage separately identifying each of the subsequent segments of theselected video program to source of the video program; and receiving thekey.
 17. The method of claim 16, further comprising the step ofdecrypting the encrypted subsequent segments with the key.
 18. Themethod of claim 1, wherein each of the segments is encrypted so as to bedecryptable by a different key before being received and stored in thelocal storage device, and the method further comprises the steps of : inresponse to the user command, transmitting a message separatelyidentifying each of the segments of the selected video program to asource of the video program; and receiving the different key for each ofthe segments.
 19. The method of claim 18, further comprising the step ofdecrypting the encrypted segments with the different key associated witheach segment.
 20. An apparatus for providing a video program to a user,wherein the video program is repeatedly transmitted on one of aplurality of channels, each repeated transmission temporally separatedfrom a previous transmission by a retransmission interval and beingtransmitted on a different channel than the previous transmission, theapparatus comprising: means for receiving and storing a first segment ofa selected video program in a local storage device before accepting auser command to view the selected video program, wherein a temporallength of the first segment is substantially equivalent to theretransmission interval; and means for retrieving the stored firstsegment for presentation to the user while receiving and storingsubsequent segments of the video program from at least one of theplurality of channels transmitting the selected video program afteraccepting the user command to view the selected video program.
 21. Theapparatus of claim 20, further comprising: means for selecting theselected video program from a plurality of video programs for video ondemand (VOD) service.
 22. The apparatus of claim 21, wherein the meansfor selecting the selected video program from a plurality of videoprograms for VOD service comprises: means for scanning a program guidehaving an entry for each of the video programs for a VOD serviceindicator; and means for identifying a video program associated with theVOD service indicator as the selected video program.
 23. The apparatusof claim 22, wherein the program guide is stored in the local storagedevice.
 24. The apparatus of claim 22, wherein the means for selectingthe selected video program from a plurality of video programs for VODservice comprises: means for accepting a selection of at least one ofthe video programs for VOD service; and means for associating the VODindicator with the entry of each video program selected for VOD service.25. The apparatus of claim 24, wherein the selected video program isselected from a plurality of video programs for VOD service by the userand the apparatus further comprises means for presenting the programguide to the user.
 26. The apparatus of claim 21, wherein the means forselecting the selected video program from a plurality of video programsfor VOD service comprises: means for scanning a program guide having anentry for each of the plurality of video programs to identify at leastone video program scheduled to be repeatedly transmitted on one of aplurality of channels, each repeated transmission temporally separatedfrom a previous transmission by a retransmission interval and beingtransmitted on a different channel than the previous transmission; andmeans for selecting the identified video program as the selected videoprogram.
 27. The apparatus of claim 26, wherein the means for scanningthe program guide comprises means for comparing video programinformation for each of the entries, wherein the video programinformation comprises a program title.
 28. The apparatus of claim 26,wherein the means for scanning the program guide comprises means forcomparing video program information for each of the entries, wherein thevideo program information comprises a unique program identifier.
 29. Theapparatus of claim 20, wherein the means for receiving and storing afirst segment of a selected video program in a local storage devicecomprises means for receiving data representing the first segment of thevideo program from a program source in a receiver communicativelycoupled to the local storage device at a time scheduled by the programsource.
 30. The apparatus of claim 20, further comprising means forsplicing the subsequent segments to the first segment for presentationto the user in response to the user command.
 31. The apparatus of claim30, wherein the video segments each comprise a plurality of videosub-segments each sub-segment associated with a time code, and the meansfor splicing the subsequent segments to the first segment forpresentation to the user comprises means for sorting the sub-segments inaccordance with the time codes.
 32. The apparatus of claim 31, whereinthe time code is an SMPTE time code.
 33. The apparatus of claim 31,wherein the time code is a program time stamp.
 34. The apparatus ofclaim 30, wherein the video segments each comprise a plurality of videosub-segments, each sub-segment associated with a time code and a channelidentifier, and the means for splicing the subsequent segments to thefirst segment for presentation to the user comprises: means forassembling the sub-segments by the associated channel identifier; andmeans for sorting the assembled sub-segments in accordance with the timecodes.
 35. The apparatus of claim 20, wherein each of the subsequentsegments is encrypted so as to be decryptable with a key before beingreceived and stored in the local storage device, and the apparatusfurther comprises: means for transmitting a message separatelyidentifying each of the subsequent segments of the selected videoprogram to source of the video program in response to the user commandand while retrieving the stored first segment for presentation to theuser; and means for receiving the key.
 36. The apparatus of claim 35,further comprising means for decrypting the encrypted subsequentsegments with the key.
 37. The apparatus of claim 20, wherein each ofthe segments is encrypted so as to be decryptable by a different keybefore being received and stored in the local storage device, and theapparatus further comprises: means for transmitting a message separatelyidentifying each of the segments of the selected video program to asource of the video program in response to the user command; and meansfor receiving the different key for each of the segments.
 38. Theapparatus of claim 37, further comprising means for decrypting theencrypted segments with the different key associated with each segment.39. An apparatus for providing a video program to a user, wherein thevideo program is repeatedly transmitted on one of a plurality ofchannels, each repeated transmission temporally separated from aprevious transmission by a retransmission interval and being transmittedon a different channel than the previous transmission, the apparatuscomprising: a tuner for receiving a first segment of a selected videoprogram before accepting a user command to view the selected videoprogram, and for receiving subsequent segments of the video program fromat least one of the plurality of channels transmitting the selectedvideo program after accepting the user command to view the selectedvideo program, wherein a temporal length of the first segment issubstantially equivalent to the retransmission interval; a storagedevice for storing the received first segment before accepting the usercommand to view the selected video program and for retrieving the storedfirst segment for presentation to the user while storing the receivedsubsequent segments of the video program after accepting the usercommand to view the selected video program.
 40. The apparatus of claim39, wherein the selected video program is selected by a control center.41. The apparatus of claim 39, wherein the selected video program isselected by the user.
 42. The apparatus of claim 39, further comprisinga transport module for splicing the subsequent segments to the firstsegment for presentation to the user in response to the user command.43. The apparatus of claim 42, wherein the video segments each comprisea plurality of video sub-segments each sub-segment associated with atime code, and the transport module sorts the sub-segments in accordancewith the time codes.
 44. The apparatus of claim 43, wherein the timecode is an SMPTE time code.
 45. The apparatus of claim 43, wherein thetime code is a program time stamp.
 46. The apparatus of claim 42,wherein the video segments each comprise a plurality of videosub-segments, each sub-segment associated with a time code and a channelidentifier, and the transport module assembles the sub-segments by theassociated channel identifier and sorts the assembled sub-segments inaccordance with the time codes.
 47. The apparatus of claim 39, whereineach of the subsequent segments is encrypted so as to be decryptablewith a key before being received and stored in the local storage device,and the apparatus further comprises: a modem for transmitting a messageseparately identifying each of the subsequent segments of the selectedvideo program to source of the video program in response to the usercommand and while retrieving the stored first segment for presentationto the user; and wherein the tuner receives the key.
 48. The apparatusof claim 47, further comprising a decryptor for decrypting the encryptedsubsequent segments with the key.
 49. The apparatus of claim 39, whereineach of the segments is encrypted so as to be decryptable by a differentkey before being received and stored in the local storage device, andthe apparatus further comprises: a modem transmitting a messageseparately identifying each of the segments of the selected videoprogram to a source of the video program in response to the usercommand; and wherein the tuner receives the different key for each ofthe segments.
 50. The apparatus of claim 49, further comprising adecryptor for decrypting the encrypted segments with the different keyassociated with each segment.
 51. An apparatus for pre-storing a videoprogram to be later provided in response to a user demand to view thevideo program, wherein the video program is repeatedly transmitted onone of a plurality of channels, each repeated transmission temporallyseparated from a previous transmission by a retransmission interval andbeing transmitted on a different channel than the previous transmission,the apparatus comprising: means for receiving and storing a firstsegment of a selected video program in a local storage device beforeaccepting the user demand, wherein a temporal length of the firstsegment is substantially equivalent to the retransmission interval; andwherein portions of the first segment are received and stored on theplurality of channels in parallel.
 52. The apparatus of claim 51,further comprising means for selecting the video program, comprising:means for scanning a program guide having an entry for each of the videoprograms for a VOD service indicator; and means for identifying a videoprogram associated with the VOD service indicator as the selected videoprogram.
 53. The apparatus of claim 51, further comprising means forselecting the selected video program, comprising: means for accepting aselection of at least one of the video programs for VOD service; andmeans for associating the VOD indicator with the entry of each videoprogram selected for VOD service.
 54. The apparatus of claim 53, furthercomprising means for selecting the selected video program, comprising:means for scanning a program guide having an entry for each of the videoprograms to identify at least one video program scheduled to berepeatedly transmitted on one of the plurality of channels, eachrepeated transmission temporally separated from the previoustransmission by a retransmission interval and being transmitted on adifferent channel than the previous transmission; and means forselecting the identified video program as the selected video program.55. The apparatus of claim 54, wherein the means for scanning theprogram guide comprises means for comparing the video programinformation for each of the entries, wherein the video programinformation comprises a program title.
 56. The apparatus of claim 54,wherein the means for scanning the program guide comprises means forcomparing the video program information for each of the entries, whereinthe video program information comprises a unique program identifier. 57.An apparatus for pre-storing a video program to be later provided inresponse to a user demand to view the media program, wherein the videoprogram is repeatedly transmitted on one of a plurality of channels,each repeated transmission temporally separated from a previoustransmission by a retransmission interval and being transmitted on adifferent channel than the previous transmission, the apparatuscomprising: a tuner for receiving a first segment of a selected videoprogram in a local storage device before accepting the user demand,wherein a temporal length of the first segment is substantiallyequivalent to the retransmission interval; and a storage device forstoring the received first segment of the selected video program beforeaccepting the user demand; wherein portions of the first segment arereceived and stored on the plurality of channels in parallel.
 58. Theapparatus of claim 57, further comprising means for selecting the videoprogram, comprising: means for scanning a program guide having an entryfor each of the video programs for a VOD service indicator; and meansfor identifying a video program associated with the VOD serviceindicator as the selected video program.
 59. The apparatus of claim 57,further comprising means for selecting the selected video program,comprising: means for accepting a selection of at least one of the videoprograms for VOD service; and means for associating the VOD indicatorwith the entry of each video program selected for VOD service.
 60. Theapparatus of claim 57, further comprising means for selecting theselected video program, comprising: means for scanning a program guidehaving an entry for each of the video programs to identify at least onevideo program scheduled to be repeatedly transmitted on one of theplurality of channels, each repeated transmission temporally separatedfrom the previous transmission by a retransmission interval and beingtransmitted on a different channel than the previous transmission; andmeans for selecting the identified video program as the selected videoprogram.
 61. The apparatus of claim 60, wherein the means for scanningthe program guide comprises means for comparing the video programinformation for each of the entries, wherein the video programinformation comprises a program title.
 62. The apparatus of claim 60,wherein the means for scanning the program guide comprises means forcomparing the video program information for each of the entries, whereinthe video program information comprises a unique program identifier.